Planetary gear transmissions are widely used in a variety of industrial applications due to its good performance and low cost. This type of transmission has a small size, light weight, high load-carrying capacity, long lifespan, low noise and can be operated steadily.
The planetary gear transmissions are commonly used in medical devices to transmit high torque through a compact package. The planetary gear transmissions used as such have short operating cycles and are required to have a small size.
FIG. 1 is a sectional view of a conventional multi-stage planetary gear transmission. This planetary gear transmission includes a gearbox 100 completely made of plastic. The last stage of planetary gear transmission supports an output shaft 300 via a shaft sleeve 200. Because the gearbox 100 is completely made of plastic, an internal gear ring 400 formed on an inner circumferential surface of the gearbox 100 is also completely made of plastic, which limits the capability of the planetary gear transmission for transmitting torque.
FIG. 2 is a sectional view of another conventional planetary gear transmission. The gearbox 101 of this planetary gear transmission is made of a metal material such as steel or aluminum, which leads to high cost. In addition, a separate rolling bearing 201 is required to support the output shaft 301 which leads to a large size, complex structure and complicated manufacturing process.